Chain printer hammer control

ABSTRACT

Circuitry for controlling the hammers of a chain type printer which is effective for maintaining each hammer set or energized for a period greater than the time of one print scan (the time between alignments of successive print characters on the chain with the same print position) and less than the time of two print scans. An address, having a predetermined relationship with the address in main storage of a byte to be printed, in the form of a particular character is stored in a hammer address register; and the address in this register is applied to a set decoder for causing a hammer to be fired and is also applied to a reset decoder for causing resetting of a hammer. The decoders decode the address in the hammer address register differently so that the hammer remains set or energized for the period mentioned.

United States Patent Berglund [is] 3,680,480 [4 1 Aug. 1, 1972 [54] CHAIN PRINTER HAMMER CONTROL [72] Inventor: Neil C. Berglund, Rochester, Minn.

[73] Assignee: International Business Machines Corporation, Armonk, NY.

[22] Filed: April 26, 1971 [21] Appl.No.: 137,344

[52] US. Cl. ..101/93 C, 340/172.5 [51] Int. Cl. ..B41j 9/00, B41j 1/20, G06f 7/00 [58] Field of Search.....l01/93 C, 111, 96; 340/1725 [56] References Cited UNITED STATES PATENTS 3,211,087 10/1965 Sapino et a1 ..101/93 C 3,289,576 12/1966 Bloom et al. ..101/93 C 3,312,174 4/1967 Cunningham ..101/93 C 3,406,381 10/1968 Peyton ..340/172.5 3,443,514 5/1969 Schwartz ..101/93 C 3,467,005 9/1969 Bernard ..10l/93 C 3,602,138 8/1971 Barcomb ..101/93 C 3,605,610 9/1971 McDowell et a1. ..101/93 C 3,629,848 12/1971 Gibson ..10l/93C Primary Examiner-William B. Perm Attorney-Hanifin & Jancin and Keith T. Bleuer 5 7] ABSTRACT vCircuitry for controlling the hammers of a chain type printer which is effective for maintaining each hammer set or energized for a period greater than the time of one print scan (the time between alignments of successive print characters on the chain with the same print position) and less than the time of two print scans. An address, having a predetermined relationship with the address in main storage of a byte to be printed, in the form of a particular character is stored in a hammer address register; and the address in this register is applied to a set decoder for causing a hammer to be fired and is also applied to a reset decoder for causing resetting of a hammer. The decoders decode the address in the hammer address register differently so that the hammer remains set or energized for the period mentioned.

10 Claims, 10 Drawing Figures PATENTEDAHBI I912 SHEEI 1 UF- 7 NEIL o. BERGLUND i) ff -Li J. W

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SHEET 3 [1F 7 I l 1 1 1 111 l 111 TE REG REG 0011111015 230 H 1 H 214 I68 192 1' 11110 1 DATA DECODER H I REG :22) HAR l REG H6 1 T RESET DECODER 11o IIYOA I LP DAR I 2 LP IAR 1105 '3 l I r HAMMER 35:81? 1 f CONTROLS co1111101 I DATA J 1 REG COMPARE 244 I82 1608 ML 1 I? STORAGE SAR 11111110 PRINT I ASSEM 208 0 l I 154 1 1 BLER I60A 1 j 210 PATENTEDMW m2 SHEET '8 OF 7 SET OPTION BEGIN RESET OPTION FIGQ3b CHAIN PRINTER HAMMER CONTROL BACKGROUND OF THE INVENTION The present invention relates to a high speed, on the fly, impact printer and more particularly to a chain printer operating with print hammers each located in alignment with a print position on a form to be printed. Still more particularly, the invention relates to apparatus and circuitry for setting or firing each of the hammers in a chain type printer for precise periods of time.

A chain printer basically is a'serial printer in which successive selected print hammers are fired in sequence. Thus a common gating pulse cannot be used to assure uniformity of pulse duration for firing the hammers. One previously suggested approach to the problem of firing the hammers for approximately the same periods of time is to employ a separatesingle shot or monostable multivibrator for each hammer electromagnet; however, for this approach to be satisfactory, extremely close tolerances must be maintained in the several single shots and, even then, frequent readjustment of the single shots may be necessary. In addition, the use of a separate single shot for each of the hammers is an expensive solution to the problem.

SUMMARY OF THE INVENTION It is an object of the present invention to provide improved controls and circuitry for the hammers of an, on the fly, impact printer and more particularly for a chain printer which are eflective for firing each of the hammers for precise periods of time. More particularly, it is an object of the invention to cause the firing time to be in effect measured by or in accordance with the movement of the movable printing element, such as the chain, whereby not only is the firing time of the hammers precisely controlled but the firing time may be adjusted to be more than the time of one scan and less than the time of two scans, with a scan time being the duration between the time one character carried by the movable printing element, such as the chain, moves into alignment with a certain print position on the form to be printed and the time the next character on the movable element or chain moves into alignment with the same print position on the form.

In brief, the circuitry of the invention utilizes the unique address of a byte of print data in storage in connection with a set decoder and a reset decoder. An address having a predetermined relationship to this unique address is held in a hammer address register during the time that a particular print hammer is to be or can be set or fired, and the set decoder decodes the address held in the hammer address register in such a manner as to cause the hammer to be fired. The reset decoder decodes this address in a different manner, during a second part of a normal option time for another hammer to be subsequently fired, and causes the first hammer to be reset or have its firing electromagnet de-energized at the subsequent time.

The invention consists of the novel constructions and circuitry to be hereinafter described and claimed for carrying out the above-stated objects, and such other objects, as will be apparent from the following description of a preferred form of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view in perspective of a portion of a chain printer with which the circuitry of the invention may be used;

FIG. 2 is a schematic perspective view of drive mechanism for the chain;

FIGS. 3a and 3b when placed together, in the manner shown in FIG. 3, constitute a schematic illustration of the circuitry of the invention for causing the hammers of the printer to be fired at the appropriate times and for the appropriate duration;

FIG. 4 is a graphic illustration of the signals from a chain emitter in the circuitry of FIGS. 3a and 3b and also showing the various subscans, three of which make up a complete scan;

FIG. 5 is a graphic illustration showing the relationship between print positions and the positions of print characters on the print chain of the printer; and

FIGS. 6a and 6b, when placed together, in the manner shown in FIG. 6, constitute a graphicillustration of various signals and addresses of certain components of the circuitry shown in FIGS. 3a and 3b.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows generally and schematically parts of a chain type printer which may be controlled by the hammer controls of the present invention. A full complement of hammers is not disclosed in this figure, and the figure discloses a chain type printer in which the hammers may be shiftable to a plurality of adjacent print positions. The printer illustrated in FIG. 1 may be seen to comprise an endless character chain carrying a plurality of type elements or characters 1 12, and the chain is movably supported on a pair of spaced wheels 114 and 116. A drive shaft 118 for the wheel 114 is connected to a constant speed motor (not shown) of any conventional type. The type elements 112 make up a full set of type, and a single set or a plurality of sets of type may be included on the chain 110. A printing ribbon 120 suitably mounted on guide rollers extends about the chain 110 and may be moved relative to the chain in a conventional manner. A printing form 122 is positioned adjacent to and is adapted to be contacted by the ribbon, and the form 122 may have perforations on its edges so that a suitable drive mechanism (not shown) may move the form 122 relative to the chain 110.

A hammer array 124 comprises a plurality of individual print hammers 126, only a limited number of which are shown in FIG. 1. The hammers 126 are mounted on a hammer bar 128, and bar 128 may be moved longitudinally with respect to the chain 110 so as to give corresponding movement to the hammers 126 whereby each of the hammers 126 may be effective on difierent printing positions on the form 122. The bar 128, in this case, may be moved longitudinally by any suitable drive mechanism.

Each of the hammers 126 is operated by a push rod 130, with the individual hammers 126 being engaged by a rod 130 and moved through the operation of an electromagnet 132.

The toothed wheel 114, and thereby the chain 110, are driven from the drive motor by means of the mechanism shown in FIG. 2 which includes a pair of toothed wheels 134 and 136 and a flexible internally toothed belt 138 which extends over the wheels 134 and 136. The wheel 134 is fixed on the shaft 118, and the wheel 136-is fixed onto a shaft 140 that is in turn driven from the drive motor (not shown). An emitter drum 142 is also fixed onto the shaft 118, and the drum 142 includes slots 144 in its periphery. A magnetic transducer 146 is fixed adjacent the drum 142 and includes a projecting magnetic core 148 that in particular has its end adjacent the periphery of the drum 142. The transducer 146 also includes a coil 150 mounted on the magnetic core 148, with the arrangement being such that each of the slots-144 in the periphery of the drum 142 produces a change in current in the coil 150 as the drum 142 rotates alongwith the toothed wheel 1 l4 and along with the chain 110.

For the purpose of the present disclosure, it may be assumed that the chain 110 has 48'characters 112 in a set and the emitter drum 142 has l44 of the slots 144 therein or three slots per character, with an additional slot, or the 145th slot, indicating the start of a set of the characters 112. Any number of sets of characters 112 may e placed on the chain 110, and the physical size of the drum 142 with respect to the chain 110 is such that the drum 142 makes one complete revolution for each set of characters passing a given print position. The chain 1 is internally toothed, and the teeth within the chain 110 mesh with the teeth on the wheel 114 so that the drum 142 rotates in timed relationship with the movement of the chain 110, and the drum 142 makes one complete revolution for each set of the characters 112 passing a given print position on the form 122. More particularly, thechain 110 and the drum 142 rotate in such u'med relationship that the emitter slots 144 align with the type characters 112 on the chain 110 in each of the sets of characters. The slots 144 are aligned with the characters 112 such that there are three of the slots 144 to define subscan positions with respect to a print position on the form 122 as will be hereinafter moreclearly, described. The printer could have 132 print positions and thus be capable of printing 132 characters on a single line across the form 122. The number of hammers 126 may be 33 in number, such that each hammer 126 would service four adjacent print positions, depending on the longitudinal adjusted position of the bar 128; however, a hammer 126 could as well be provided for each of the print positions so that in this case, there would be 132 of the hammers 126. For simplicity and for the purpose of the present disclosure, it will be assumed, however, that there are only 33 print positions each in alignment with a hammer 126; and, in this case, the bar 128 is stationa- Referring to FIGS. 3a and 3b showing the controls for the printer hammers 126, the controls may be divided into the three parts 152, 154, and 156, the part 152 representing parts on the printer itself, the part 154 representing a computer from which information is derived for the purpose of operating the printer, and the part 156 representing the logic for interconnecting the computer with the printer. The part 152 includes the emitter 146, and the electromagnets 132 included in the part 152 are energized at the proper times under control of the emitter 146 and also under the control of the logic 156 so that the desired line of print is made by actions of the hammers 126 on the chain in synchronism with the proper characters 112. In particular, the part 152 includes the hammer drivers 158 which control the energization of the individual .electromagnets 132 for firing the hammers 126 to effect printing. The part 152 omits the controls for'the carriage for moving the form 122 from a position for printing one line to the next position for printing the subsequent line, such carriage controls being conventional.

The logic 154 of the printer includes components of a computer from which information is derived for the purpose of operating the printer and includes the main storage unit having auxiliary storage units 160A and 160B. A storage address register 162 is associated with the storage unit 160. The auxiliary storage unit 160A includes data for the line-to be printed by the chain 110 and hammers 126, and the storage unit 1608 includes data on the chain image or the sequence of chain characters 112 as they appear. on the chain 110. The logic 154 also includes the arithmetic logic unit 164 of the computer which functions to make a comparison of the data to be printed and the chain image to determine whether printing can be effected at any particular instant. The computer includes the A register 166 and the B register 168 which respectively store the data to be printed and the image of the character on the chain 110 at the print position being considered. The computer in part 154 of the controls also includes the LPDAR or address register 170A for the data to be printed and the LPIAR or address register 170B for the image on the chain 110 in a block of local store registers 170.

The part 156 of the printer controls effectively connects the computer in the part 154 with the parts on the printer shown in part 152 and includes a chain character counter 172 which receives signals from the emitter 146 to determine the character on the chain 110 in alignment with a print position on the form 122. Cycle steal controls 174 control the B register 168, the ALU 164, and the address registers 170 when the printer attachment receives a print command. At this time, data from the arithmetic logic unit 164 passes through a data bus out 176 to data registers 178 and 180 in the part 156 of the controls. The register 178 contains at different times the data to be printed and the print position on the form 122 at which the data is to be printed. The data register 180 receives signals from data bus out 176 when a comparison is made between a chain image character and print line data on a particular print position, and when these two data compare, it causes a hammer 126 to be fired by the associated electromagnet 132. The hammer firing signal from the data register 180 is transmitted through line 182, through AND circuit 184 which is also controlled by hammer controls 186 and hammer clock and control 188, and through line 189. The hammer clock and control 188 also has its output lead 190 connnected with the hammer address register 192 for controlling the latter. The address in data address register 170A of the print position to be printed or, more accurately, an address which has a fixed relationship to the address of the print position in storage 160, is transferred from register 178 into register 192.

Pulse signals from the chain emitter 146 are directed to the print subscan counter 194 wherein a count of the subscans is maintained. As will hereinafter more clearly appear, each time one of the characters 1 12 moves into alignment with a print position 1 on the form 122, the beginning of a subscan l is defined. Every time a character 112 moves into alignment with print position 2 on the form 122, subscan 2 begins; and subscan 3 begins when a character 1 12 moves into alignment with print position 3. A full print scan begins each time a character 1 12 moves into alignment with print position 1 (the same as the beginning of subscan l) and continues until the next character on the chain moves into alignment with print position 1. The output of the print subscan counter 194 is fed to the chain character counter 172 and in particular to a binary counter 196 and a four-bit shift register 198 in the counter 172. The binary counter 196 feeds a seven-bit shift register 200 for the purpose of counting from the home pulse each of the characters 1 12 in a set and with the identification being in binary code. The binary counter 196 is reset with respect to the home pulse derived from the chain emitter 146 by means of the home pulse detector 202 which is connected with a reset terminal of the binary counter 196. The count in the seven-bit shift register 200 is modified by the four-bit shift register 198 which in turn is controlled by the print subscan counter 194. The output of the four-bit shift register 198 is fed to an adder 204 along with the contents of the shift register 200, with the adder 204 adding the signals a bit at a time and feeding them back into the seven-bit shift register 200 such that the seven-bit shift register will provide an identification in binary code of the character 112 in the set of characters which is presently in alignment with a particular print position. The shift registers 200 and 198 are controlled by a signal from a clock 206 which shifts the registers 200 and 198. The output of the seven-bit shift register 200 is fed through bus 208 to a data bus in assembler 210 which functions to load the data into a data bus in 212 connected to the A register 166. The DB1 assembler 210 also receives the data to print from the data register 178 for purposes to be later noted.

The signal in the hammer address register 192 for selecting the hammer 126 for firing is directed to the set decode logic 214 and to the reset decode logic 216 which respectively address a hammer 126 to set it and to reset it. The output of the logic 214 is connected to AND circuitry 218, and the output of the reset logic 216 is connected to AND circuitry 220. The AND circuits 218 and 220 are connected to OR circuitry 221 which in turn is connected through bus 222 to hammer driver logic 158. The AND circuitry 218 actually includes a plurality of separate AND circuits, one for each of the address lines used for controlling the electromagnets 132. There are nine X address lines, and there are four Y address lines, making a total of 13 lines. Using one Y address line and one X address line corresponding to each AND circuit, it is possible to control each of the 33 electromagnets corresponding to the 33 printhammers. Each of the AND circuits in the circuitry 218 is controlled by the set option signal in line 224. The AND circuitry 220 is similarly onstructed, and each of the AND circuits in the AND circuitry 220 is controlled by means of a reset option signal on line 226. The OR circuitry 221 also includes the same number of individual OR circuits as AND circuits 218 (of 220). a

A flip-flop 228 is provided for controlling the AND circuits 218 and 220. The flip-flop 228 when set provides a set option signal on lead 224 applied to AND circuits 218 for enabling these AND circuits and when reset provides a reset option signal on lead 226 applied to AND circuits 220 for enabling the AND circuits 220. The flip-flop 228 is set due to a begin set option signal on lead 230 connected as an output to the hammer clock and control logic 188, and the flip-flop 228 is reset by a begin reset option signal on lead 232 also connected as an output of the hammer clock and control logic 188.

Hammer status bit storage logic 234, for at times inhibiting certain hammer reset pulses as will be described, is also connected as an output of OR circuits 221. The logic 234 is connected through a lead 236 with an inverter 238 andthereby with an AND circuit 240 which has an output 242 connected with the hammer drivers 158. The output lead 244 of the hammer clock and control logic 188 is also connected as an input to AND circuit 240. It will be observed from FIG. 3 that the hammer status bit storage logic 234 as shown in this figure has nine X address lines and four Y address lines. These address lines are the same as those previously described in connection with AND circuits 218 and 220 and OR circuits 221.

The hammer status bit storage logic 234 consists of 33 storage elements (for example, flip-flops or latches) with one corresponding to each of the hammers 126. Any of the 33 storage elements can be selectively set to an on status by selecting that storage element by raising the proper combination of X and Y address lines in bus 222 and applied onto logic 234 and at the same time providing a set pulse on line 246. Likewise, any of the storage elements that have been previously set can be reset to an ofi status by providing a reset pulse on line 248, while the particular X and Y address lines selecting that particular storage element remain on.

The set pulse on line 246 is provided by an AND circuit 250 which has as inputs the compare line 182 and the line 190 constituting an output of hammer clock and control 188. The reset pulse on line 248 is provided by AND circuit 252, which has the line 190 as an input and which also has as an input the output of an inverter 254. The inverter 254 is controlled from the line 182.

During operation of the printer, the emitter 146 provides an emitter signal indicating the position of the chain, and printing is under the direct control of the emitter and is thus synchronized with the movement of the chain 110. FIG. 4 may be referred to for a showing of the pulses from the emitter 146 and for a corresponding showing of the times during which subscans l, 2, and 3 occur, referenced to the emitter pulses. It may be assumed that there are 33 print positions in alignment with 33 hammers 126. Ifit is desired that the hammers may be moved to service a plurality of print positions on the form 122, shifting of the hammers may be accomplished as disclosed in the co-pending application of N. C. Berglund et al., Ser. No. 51,190, filed June 30, 1970. During each subscan of the 3 subscans in each print scan, one-third of the 33 print hammers 126 are optioned to print, that is, if the proper character 112 is before the particular print hammer during the subscan, the hammer can print this character onto the form-122. Therefore, during the print scan consisting of subscans 1, 2, and 3, all 33 hammers 126 are optioned to print; and, during each scan, each hammer 126 is presented with one character 112 on the chain 110. The chain and print position spacings are such that only one print hammer 126 has a character 1 12 aligned with it at any one instant of time. This may be accomplished by having the type spacing on the chain 10 approximately 1 times the spacing between print positions on the form 122 and by having the characters 112 slightly out of alignment with print positions as by so constructing the chain 110 and placing the characters 112 so that, for example, the character under print position 4 is 0.001 inch out of alignment with this-print position when a character 1 12 is aligned with print position 1. FIG. may be referred to for a showing of the print positions on form 122 and for a showing of the characters 112 on the chain 110. There is a hammer 126 (not shown) aligned with each of the print positions. It may be assumed that the A character 1 12'is in alignment with a print position 1 at the beginning of subscan l; and, therefore, the characters C, E, G, and l are successively in greater disalignment with print positions 4, 7, 10, and 13, as shown. At the beginning of subscan 2, the B character 112 has moved from its position between print positions 2 and 3 into alignment with print position 2, and the other characters 112 have moved accordingly. At the beginning of subscan 3, the C character 112 has moved into alignment with print position 3, as shown.

In order to present a character 112 to every hammer 126 in each print scan, the hammers 126 are optioned one at a time in a definite order; and each hammer 126 will be optioned at exactly the same time in every print scan. More particularly, in a particular embodiment of the printer, the hammers may be optioned as shown in the following table (Table 1):

TABLE 1 Subscan 1 Subscan 2 Subscan 3 Hammer Hammer Hammer As will be observed from Table 1, hammers Nos. 1, 4, 7, 10, 13, 16, 19,22, 25, 28, and 31 are successively optioned in subscan 1 so that all of these hammers will print one after the other in the order just given, assuming that the proper character 112 is positioned at the time in alignment with the hammer. During subscan 2, the hammers Nos. 2, 5, 8, 11, 14, 17, 20, 23, 26, 29, and 32 are optioned; and likewise, during subscan 3, hammers 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, and 33 are optioned.

The present invention maintains each of the hammers 126 set or on, once'the hammer has been energized, for a length of time which is greater than one scan time but which is less than two scan times; and this is accomplished under the'control of the emitter 146 which is synchronized with the movement of the chain 110. This has been accomplished by the present invention by breaking the normal option time for a hammer 126 into two parts. The normal option time is the time from the alignment of some character 112 and a print position on form 122 until the next print position to be serviced in that subscan has a character 112 aligned with it. For example, referring to FIG. 5, the character A is in alignment with print position 1. The next character in subscan 1 to move into alignment with a print position is the character C, which will move into alignment with print position 4. The time required for the character C to move into alignment with print position 4 just after the letter A aligns with print position 1 is a normal option time. In a particular printer, the normal option time may, for example, be 4.8 microseconds. The first part of the normal option time is used to service a hammer 126 as usual, and this may be just one half of the normal option time, for example, 2.4 microseconds. The second part of the normal option time, which in the particular example is 2.4 microseconds, is used to address another hammer 126 for the purpose of resetting this other hammer 126, assuming that the latter hammer has been previously set, for example, in a previous scan.

The following Table 2 supplements Table 1 in that Table 2 also shows the hammers 126 which may be reset during subscans 1, 2, and 3; and thefollowing Table 3 shows substantially the same as Table 2, but in another form:

TABLE 2 Sequence of Hammer Optioning Subscan l Subscan 2 Subscan 3 1 Set Reset Set Reset Set Reset Option Option Option Option Option Option TABLES Sequence of Hammer Addressing PSSl 147 10 13 16 19 22 25 28 3'1 SEIOPTION 8111417202326293236 RESET OPTION PSS2258lll4172023262932 SETOPTION 9121518212427303314 RESET OPTlON P88336912 18 212427 3033 SEIOPTION 7101316192225283125 RESET OPTION PSSl 147 10 13 1619 22 2s 28 3.1 sEroPnoN 8111417202326293236 RESET OPTION PSS2258ll14172023262932 SETOPTION 91215182124273033l4 REsET OPTION lt should be noted here that Tables 1, 2, and 3 are applicable for 33 print positions with a hammer 126 per print position on form 122 as described above, and they are also applicable for 132 print positions on 'form 122 where each of the 33 hammers covers 4 adjacent print positions as in the printer described in the co-pending application of N. C. Berglund et a1., Ser. No. 51,190, filed June 30, 1970.

As above described, hammers Nos. 1, 4, 7, etc., are set or optioned in subscan l; hammers Nos. 2, 5, 8, etc., are set or optioned in subscan 2; and hammers Nos. 3, 6, 9, etc., are set or optioned in subscan 3. Tables 2 and 3 show that just after a set option is supplied for hammer No. l, a reset option is supplied for hammer No. 8. Subsequently, a set option is provided for hammer No. 4 and immediately thereafter a reset option is provided for hammer No. l 1, etc. In subscan 2, a set option is provided for hammer No. 2 and immediately thereafter a reset option is provided for hammer No. 9, etc. The sequence of the other set options and reset options are apparent from Tables 2 and 3. It will be observed that the reset option for hammer No. 1 occurs near the end of the second subscan, and it would be possible to de-energize the electromagnet 132 for hammer No. 1 at this time, approximately twothirds of a scan; however, preferably this eletromagnet 132 is maintained energized for more than one scan and in particular for 1 scans, so therefore, circuitry is provided so that the reset signal 242 for hammer No. 1, occurring less than one full scan after the electromagnet 132 for this hammer is energized, is inhibited so that the electromagnet is actually maintained energized for about 1 scan. As will be hereinafter described in greater detail, the reset decoder 216, the hammer status bit storage logic 234, and associated circuitry provide this resettingaction for a hammer 126; and, as will be obvious, the structures of the decoder 216 and hammer status bit storage logic 234 could be changed as desired so as to change the energized time for an electromagnet 132 to other than 1 scan.

In the operation of the printer, the chain emitter 146 drives the chain character counter 172 so that counter 172 maintains a count corresponding to the position of the chain 110. More particularly, the binary counter 196 maintains a count in binary code of the number of characters 112 in a type set. If a 48 character type set, for example, is used, the counter 196 will count from 0 to 47 as each of the chain characters 1 12 passes a given print position, for example, the first print position. The

first print subscan pulse for each character 112 in a set as sensed by the emitter 146 is used to activate the counter 196, and at the end of a set of characters 112 as evidenced by a complete revolution of the timing drum 144, a home pulse is received and is sensed by the home pulse detector 202, the output of which is used to reset the counter 196. 1

The output of the counter 196 is broadsided into the seven-bit shift register 200 wherein it is modified according to the subscan existing in order to maintain a count in binary code in register 200 of the type character 112 approaching the print position under consideration. The modification according to the particular subscan is provided by the four-bit register 198 which receives signals from the print subscan counter 194. For this purpose, the print subscan counter 194 in serts a 1 into the four-bit'shift register 198 for subscan 2, and inserts a 2 into the shift register for subscan 3. 1f subscan .1 existed, a 0 would be inserted in the four-bit shift register 198. This initialization provided by the print subscan counter 194 to the four-bit shift register 198 is provided at the start of each subscan. The numbers 0, l, and 2, fed in binary code to the four-bit shift register 198, are added serially a bit at a time with the numbers from the seven-bit shift register 200, and the result modifies the output of the seven-bit shift register 200 to correct the same so as to give it true indication of the number of the type character 112 at the print position at the start of any subscan at which a first hammer 126 may be fired. Furthermore, as each subsequent hammer 126 is serviced, the seven-bit and four-bit shift registers 200 and 198 are used to modify the contents of the seven-bit shift register by an increment factor of +2 so that the seven-bit shift register 200 holds a number indicating the chain character 112 aligned with the hammer being serviced. The initialization factors and increment factors for the four-bit shift register 198 are different if each hammer covers four adjacent print positions. This is completely described in the co-pending application of N. C. Berglund et aL, Ser. No. 51,190, filed June 30, 1970; and it is also clear from the disclosure of this co-pending application how in detail the initialization and increment factors are inserted into the four-bit shift register 198.

The output of the seven-bit shift register 200 is applied to the DB1 assembler 210 for controlling the remainder of the circuitry so that proper printing takes place. The clock 206 controls the action of the two shift registers 198 and 200 and the clock 206 is by any conventional means synchronized with the pulses derived from the chain emitter 146 so that, in effect, the action of the shift registers 198 and 200, and for that matter all of the other parts in the system, are synchronized with pulses from the chain emitter 146.

The circuitry in order to fire any given hammer 126 utilizes the data desired to be printed on the form 122 and data of a character 112 on the chain 110. The data that is to be printed is contained in the storage unit 160A, and the image of the chain is contained in storage unit B. The chain image in the storage unit 160B is constant for the particular chain 110 or chain cartridge mounted on the printer. If another type of chain 110 with difl'erent characters on it is desired to be used, then it is necessary to reload the chain image in the storage unit 160B. The data that is contained in the storage unit 160A is constant for the duration of a line of print on the form 122. After a complete line has been printed by the characters 112 on form 122, the area 160A is blank; and, at this time, the storage area 160A is loaded with the data for the next line of print to be made on the form 122.

The circuitry causes a comparison to be made between the data to be printed in a given print position on the form 122 and the chain image character 112 that is presently positioned in front of the same print position on the form 122; and, if there is a compare, the

' circuitry causes the corresponding hammer 126 to be fired in order to print the character 1 12 in that particular print position. In order to make a print comparison, the circuitry must have indicated to it which particular position of the 33 position positions (assuming 33 print hammers are used in the printer) is presently being serviced and which of the chain characters 112 is in alignment with that print position. The pring positions are scanned in sequential order, and the counter 172 indicates the particular character 112 on the chain 110 that is in alignment with the print position being serviced. The contents of the shift register 200 is thus used to address for the particular chain image character that is contained in the main storage unit 160B.

For the printing operation, the data for a given print position on the form 122, for example, print post position 1, is extracted from storage unit 160B and is passed through the B register 168 and the ALU 164 to the data register 178. On the next memory cycle in the CPU (shown in controls part 154), the chain image character that is presently positioned in front of print position 1 is removed from main storage 160 and particularly from the portion 160B thereof and is loaded in the B register 168. At the same time, the data character which was previously loaded into the data register 178 is sent back to the CPU through the DB1 assembler 210 and is loaded in the A register 166. Therefore, at this time, the data to be printed is present in the A register 166, and the chain image is present in the B register 168. These two bytes of data are then subtracted to determine whether or not they compare, and this is accomplished by the action of the ALU 164. The output of the ALU is if the two bytes are equal. The result of the subtraction by the ALU 164 is sent through the DB0 bus 176 and is decoded in data register 180. The 0 result will be indicated on the compare line 182, and the signal on line 182 is ANDed with a timing pulse on line 190 generated to set the corresponding one of the hammer drivers 158.

The cycle steal controls logic 174 controls the memory cycles in theCPU (in part 154) and also controls the retrieval of the chain image and the data byte that is to be printed from storage 160. As just described, the data byte and the chain image are retrieved from storage 160 on successive memory cycles, and the logic 174 controls the retrieving of this data, determining that it-is gated into the proper registers, that the data and image byte are subtracted in the ALU 164, and that the results are sent to the data register 180 in proper timing so as to determine whether or not there is a compare of the two sets of data.

The hammers 126 must each be fired at a precise instant and time, that is, when the moving chain characters 112 are in exact with the print positions that are to be printed; and it is the function of the hammer controls 186 and hammer clock and control 188 to determine this precise instant at which each.

hammer 126 must be fired. The output from the hammer clock and control logic 188 in line 190 is the timed pulse which occurs at the instant that a given hammer 126 has a character aligned under it. If the compare signal on line 182 exists, this timing pulse then becomes a set signal applied through AND circuit 184 to the particular hammer driver 158 for the particular hammer 126 being considered.

The hammer address register192 and the hammer address set decoder 214 are used to select the proper hammer 126'to be fired, that is, the hammer 126 that corresponds to the print position that is presently being serviced. For example, if the data in print position l location in main storage 160 is being considered to determine what character shall be printed in print position 1 on form 122, the hammer address register 192 and the decoder 214 conditions the proper address lines 222 for a hammer 1, so that this hammer is addressed when servicing print position 1. As other print positions from 1 33, corresponding to the 33 hammers, are serviced, the hammer address set decoder 214 conditions the proper address lines 222 such that each of the 33 hammers is addressed in turn.

In the above described transfer of data from main storage 160 and the portions 160A and 160B thereof, the local store registers 170 and particularly the LPDAR 170A and the LPIAR 170B function to address the contents of main storage 160. The LPDAR holds the address in storage 160 where the data corresponding to the various print positions on the fonn 122 may be found. The LPIAR holds the address in storage 160 where the image of a particular character on the chain may be found. If the chain 110 has 48 1 characters, for example, the 48 characters on the chain 110 are assigned the numbers 0 47, and these 48 numbers are incremented in the shift register 200 under the control of pulses from the chain emitter 146. These numbers 0 {47 are loaded into the LPIAR local storage register 170, and these numbers as so loaded then become the address in storage where the actual code of that that character on the chain 110 may be located. For example a numeric 1 may be the first character on the chain 110 and its address in LPIAR local store register is then 0. In location 0 in main storage 160 is located the code for the numeric 1. Likewise, the LPDAR local store register 170A holds the address in storage 160 where may be located the code of the data character that should be printed.

The first print position on the form 122 has thus been serviced. If there is a compare of the two sets of data, the data corresponding to the particular character 112 on chain 110 in alignment with print position 1 with the character that should be printed in print position 1, a compare signal exists on line 182 and the first hammer 126 is set to cause printing to take place. On the other hand, if there is no compare, the print hammer 126 in the first print position is not fired. After the first hammer has thus been serviced, the next print position is serviced where the fourth hammer is located. The

cessed and is moved through the B register 168 and ALU 164 to the data register 178. At this time, the character 112 on the chain 110 that is in front of this particular print position must be indicated by the circuitry, and the counter 196 and shift register 200 function together for so indicating the character. The information from the shift register 202 is supplied through the DB1 assembler 210 and the DBI bus 212, and the information passes through the A register 166 and is loaded in the LPIAR local store register 170A. The information in the LPIAR register is then used to address storage 160 so as to bring out the actual coding for the image character that the circuitry is now concerned with, and this coding is put into the B register 168 and a comparison is made as before.

The circuitry continues to scan the line of print on form 122 on which printing shall be accomplished, and each of these print positions is in effect compared with the character 112 on chain 110 that is presently aligned in each print position in making the decision whether or not a printing shall be accomplished at that specific print position. The print positions listed in print subscan 1 in Table l are first consecutively scanned, namely print positions 1, 4, 7 31; then the print positions listed in print subscan 2, namely print positions 2, 5, 8, ll 32, are consecutively scanned; and finally, the print positions in print subscan 3 are consecutively scanned, namely print positions 3, 6, 9 33. After all 33 print positions (assuming that there are 33 print positions on the form 122 and that there is a hammer in alignment with each printposition) have been serviced, there has at that time been presented one character 112 on chain 110 to each of the 33 print positions. If a comparison would have occurred for one or more of the print positions, the corresponding hammers 126 would have fired, printing characters 112. After the first scan has thus been completed, moving character A, for example, out of alignment with print position 1 and moving the next character, for example, character B, into alignment with print position 1, an additional scan consisting of three more subscans is similarly taken, and the initial procedure for the first scan is repeated 47 more times after the first scan, so that each of the 48 characters 112 on the chain 110 is presented to each of the 33 print positions; and printing of the particular line of 33 print positions on the form 122 is completed.

As has been previously briefly mentioned, the present invention only de-energizes a hammer electromagnet 132 after a period which is greater than the time of one scan and is less than the time of two scans has expired. This is accomplished basically by causing each of the hammers 126 to be addressed twice in each print scan. A particular hammer 126 is addressed when a character 1 12 moves into alignment with a print position (at a time called option to set) and again approximately two-thirds scan later (at a time called option to reset). The exact time in a scan at which a hammer is optioned to reset occurs is determined by the desired hammer on time. Each normal hammer address interval is divided into two parts, but the duration of each part is not significant. The first part becomes the option to set for one of the hammers 126 and the second part becomes the option to reset for another of the hammers 126. Referring again to Tables 2 and 3, it is apparent that the first hammer that has an option to set is hammer No. 1 and this option occurs in the first part of a normal hammer address interval (prior to hammer No. 4 being given an option to set). During the second part of the first normal hammer address interval, hammer No. 8 is given an option to reset, and this reset option is significant only if hammer No. 8 has been set in a previous print scan. Likewise, all of the other hammers 126 have options to set and reset in the two parts of normal hammer address intervals.

When each hammer is addressed during the first part of a normal hammer address interval which includes one option to set and one option to reset as above described, a character 112 moves into alignment with the particular hammer and a binary number corresponding to the hammer is loaded into the hammer address register 192. The binary number that is loaded into register 192 at this time constitutes the address used for accessing the data from the main storage unit that is to be printed. The binary number that is loaded in register 192 is the current value in the data address register A which was passed on DB0 176 to register 178 and thence to register 192. The data in register 170A is also used to address main storage 160A for the print data, as was previously described. Thus, no separate counter is required to generate hammer addresses, as the contents of register 170A have a fixed relationship to the hammer to be addressed. This number is decoded by the two difierent decoders 214 and 216. During the set option interval (the first part of the normal address interval), the output of the set decoder 214 causes the particular hammer to be addressed, such as hammer No. 1 in the particular example just given. FIGS. 6a and 6b illustrate the timing in connection with the optioning to set of hammer No. l and the timing of other operations occurring at about the same time.

It will be observed from FIGS. 6a and 6b that, during the first part of a subinterval a (which is a normal hammer address interval) in subscan 1 of print scan N, the contents of the hammer address register 192 is 011111, for example, which is the address in storage 160 of the data to be printed by hammer No. l in print position 1. This numeral may be divided into an X component of 01 1 l and a Y component of 1 l, and this content of the HAR register 192 is decoded by the set decoder 214 to provide a hammer address of X7 and YC, for example, which corresponds to hammer No. 1. As described, a hammer address may be made up of an X address and a Y address, such as X addresses of X7, X8, X9, XA, XB, S XC, XD, XE, and XF; and Y addresses of Y0, Y4, Y8, and YC.

During the following second part of the normal hammer address interval (the last part of subinterval a), during which the contents of the HAR register 192 remain 011111, the reset decoder 216 is operative to decode these contents of the HAR 192. The decoder 216 operates difl'erently from the decoder 214 and provides the address of hammer No. 8 which is X9 and Y8. Thus, during the first normal hammer address interval of subscan 1, the address of hammer No. 1 is first produced and then the'address of hammer No. 8 is next produced as is indicated also in Tables 2 and 3.

Immediately after subinterval a, and during subinterval b, in subscan 1 of print scan N, the contents of the HAR 192 is changed, and under these conditions the l set decoder 214 will produce the address of hammer No.4 and just subsequently thereto in the second part of the subinterval, the set decoder 216 will produce the address of hammer No. 1 l, as is shown in Tables 2 and 3. Likewise, the other subintervals in subscans 1, 2, and 3 of print scan N will produce the addresses of the other hammers which are indicated in Tables 2 and 3. More particularly, during the last part of subscan 2 in 7 print scan N, in the next to the last subinterval, the contents of the HAR'192 may be 111011, as shown on FIGS. 6a and 6b. The decoder 214 with these contents of the HAR 192 will produce the address of hammer No. 29 of XE an and YC in the first part of the normal hammer address interval. During the second part of this normal hammer address interval, the reset decoder 216 will produce the address of hammer No. l, which is X7 and YC. v

For the following print scans of N l and N 2, etc., the contents of the HAR 192 will change in exactly the same manner as in print scan N, and the same hammer addresses will be produced by the decoders 214 and 216.

The set option signal on line 224 and the reset option signal on line 226 occur respectively during the first and second parts of the print subscan subinterval as shown in connection with print subscan l of print scan N in FIGS. 6a and 6b. Therefore, if there is a compare signal on line 182,'AND circuits 218 and 184 will provide a firing or setting of hammer No. l in the example given, particularly by the hammer address signals 222 during the set option signal on line 224 shown in FIGS. 6a and 6b so that hammer No. 1 is set at the beginning of the hammer set pulse 189. On a setting of hammer No. 1, the hammer status bit storage logic 234 having the hammer address of Y7, XC applied thereto has a storage element or latch thereof set and produces a hammerstatus bit on line 236 which is shown under print subscan 1 of print scan N in FIGS. 6a and 6b. The hammer status bit exists at this time on line 236 in particular because a compare exists on line 182, which is an input to AND circuit 250. The other input to AND circuit 250 is a timing signal on line 190 which exists at this time.

As shown in FIGS. 6a and 6b, during print subscan 2 in print scan N, the HAR 192 contents of 111011, decoded by decoder 214, produces the address of hammer No. 29 in the first part of the normal hammer address interval, and the decoder 216 produces the No. l hammer address of X7 and YC in the second part of the normal hammer address interval. The hammer status bit on lead 236 for hammer No. 1 remains effective, and therefore at this time there is no hammer reset pulse on line 242; and hammer No. 1 remains set through the remainder of subscan 2 and also during subscan 3 of print scan N. During scan 1 of print scan N 1, hammer No. l is again serviced during the first part of thenormaladdress interval. At this time, the hammer status bit corresponding to hammer No. I will be set to an off status because no compare can exist for hammer No. l at thistime. Hammer N0. 1 was energized in print scan N when a compare existed. During print scan N l, the compare does not exist and therefore AND circuit 252 acts to reset the hammer status bit corresponding to hammer No. 1. AND circuit 252 is conditioned by a timing signal on line 190 and by the absence of a compare signal on line 182 so that inverter 254 provides an input to AND circuit 252.

Hammer No. 1 is again addressed during the second part of a normal hammer address interval, near the end of the print subscan 2 in print scan N 1 and while the reset option signal on lead 226 is up. At this time, a resetting of hammer No. I does take place, a hammer reset pulse on lead 242 being produced by the reset clock signal on lead 244, inasmuch as the status bit signal on lead 236 does not now exist whereby AND circuit 240 is rendered efiective. Hammer No. I has therefore remained set for about 1 scans which may be about 1.2 milliseconds for a particular printer as is indicated in FIGS. 6a and 6b.

The others of the hammers 126 are likewise held set for about 1 scans or 1.2 milliseconds for the particular printer mentioned in the same manner as is hammer No. l.

The address contained in the HAR register 192 and which is decoded by the decoders 214 and 216 for producing the setting and resetting address for hammers 126 may be exactly that address which accesses the data to be printed from main storage 160. On the other hand, the address in the HAR register 192 may be a diflerent address but one which has a fixed relationship with the address which accesses the data to be printed from storage 160. For example, if hammer No. l is being used in connection with print position 1, the hammer No. 1 address for data to be printed of O1 1 1 10 may not itself be inserted into the HAR register 192,

' but instead the address for hammer No. 4, the next hammer to be optioned to set, which is 100010, for example, may be inserted into hammer address register 192. The decoders 214 and 216 in this case are so constructed as to energize the hammer address lines of X7, YC even though the contents of the HAR 192 is actually the data address of hammer No. 4, instead of hammer No. 1. Certain economics in logic design may be accomplished in certain circumstances by actually using a different data address to generate the hammer address lines than the actual address of the hammer under consideration; but in any case, there is a definite relationship between the address used at this time in the HAR register 192 and the actual address of the print data in main storage under consideration; and, in particular, the address used in'l-IAR 192 is the address in storage for a certain hammer 126 which is a certain number of hammers earlier or later in the option and firing sequence.

In summation, the normal option time for any particular hammer 126, which is one of the subintervals in each of the subscans referred to in connection with FIGS. 6a and 6b, has in eflect been broken into two parts by the circuitry of the invention. The first part is used to service a particular hammer, to compare a character to be printed along with the character 112 on the chain actually in alignment of with a print position, and the circuitry of the invention causes the second part of the normal option time to be used to address another hammer and to reset this other hammer if the other hammer has been previously set. Each byte of data to be printed contained in the storage unit 160A has a unique address in the storage unit 160A associated with it, and this address has a direct relation to the particular hammer 126 being serviced. Consequently, the address used to retrieve the print data from the storage part 160A can also be used to generate the corresponding hammer address lines (X7 and YC, for example, for hammer No. l), and the set decoder 214 causes this action to take place. Since each of the hammers 126 is addressed a known time after the beginning of a particular subscan, and since, in particular, each of the hammers 126 is addressed a second time during the second part of a normal option time, this fact can be used to determine at which-time to reset each of the hammers 126. Thus again, the invention uses the address which is used to retrieve print data from the main storage part 160A to be used also to generate the address lines of the hammer which is to be reset, the reset decoder 216 in particular using the contents of I-IAR 192 for this purpose as above described.

For a particular high speed chain printer, which is capable of printing 300 lines per minute, the scan time is 0.729 milliseconds. With previous relatively slow speed chain printers having a scan time of 1.167 milliseconds, the 1.167 milliseconds has proved to be a sufficient time for energizing a print hammer; however, the 0.729 milliseconds has proved to be too short a period for hammer energization for obtaining satisfactory printing. Two full scans could instead be relatively easily used for hammer energization; however, such relatively long energization times would cause overheating of the electromagnet 132 associated with a particular hammer. The present invention, therefore, includes circuitry for energizing a print hammer for approximately 1 scans or about 1.2 milliseconds which is sufficient time to provide good printing but which is short enough so that overheating of the electromagnet 132 does not take place.

The invention therefore utilizes the inherent timing relationship of the chain 110 for determining accurately the resetting times for the hammers 126. The electromagnet 132 for each hammer 126 is therefore caused to be energized for a precise period of time for firing the hammer without the use of separate counters or single shots for each hammer which would not only be relatively expensive but would also be less precise and accurate in action.

I wish it to be understood that the invention is not to be limited to the specific constructions and circuitry shown and described, except only insofar as the claims may be so limited, as it will be apparent to those skilled in the art that changes may be made without departing from the principles of the invention.

In particular, it is to be understood that although I have specifically described a resetting of each of the hammer 126 after a duration of set of about 1 scan times, resetting according to the principles of the invention could instead be accomplished for more than a plurality of scans or for less than a full scan. For slower speed printers, a resetting could well be desirable for less than a single scan, and this may be accomplished under the control of movement of chain 110 by not utilizing the hammer status bit storage 234 which inhibits the hammer reset pulse 242. On the other hand, delay means could be utilized in connection with the hammer status bit storage logic 234 for delaying the cessation of the hammer status bit 236 so that it remains up also during print scan N l and possibly additional scans, referring to FIGS. 6a and 6b, so as to reset a hammer 126 later than two scans after firing.

What is claimed is:

1. A high speed printer comprising, in combination:

a moving type carrier having a series of print characters thereon,

a print hammer disposed to impact with said type carrier for printing said print characters in a print position located in alignment with said hammer,

a hammer driver motor for firing said hammer upon being energized,

' means for driving said type carrier so as to move said print characters successively into alignment with said hammer with a print scan being determined from the time when one print character of the type carrier ,is in alignment with said hammer to the time when the next print character on the type carrier is in alignment with said hammer,

means acting in timed relationship with the movement of said type carrier for selectively energizing said motor so as to fire said hammer,

timing means synchronous with the movement of said type carrier for producing a signal which is subsequent to the firing of said hammer by a time different than one print scan duration, and

means responsive to said signal for de-energizing said motor within the duration of said last-named print scan.

2. A high speed printer as set forth in claim 1, said hammer driver motor constituting an electromagnet.

3. A high speed printer as set forth in claim 2, said type carrier constituting an endless chain.

4. A high speed printer as set forth in claim 3, said printer including additional print hammers disposed in a line with said first-named print hammer and each actuated by an electromagnet, said electromagnets for said additional print hammers being energized and being de-energized by the same means as the electromagnet for said first-named print hammer.

5. A high speed printer as set forth in claim 4, and including a storage unit having a section for storing data to be printed by said hammers and also including a section for storing the images of the chain characters passing the various print hammers, and means for comparing the chain images and the data to be printed and for energizing the respective electromagnets to fire the respective hammers when there is a compare.

6. A high speed printer as set forth in claim 5, said data to be printed and said chain images in said storage unit each having an address, means for storing an address which has a definite relationship to and is derivable from the address in said storage unit of the data to be printed, said means acting in timed relationship with the movement of said type carrier including a decoder which has the address in said register applied thereto to selectively energize said electromagnets for firing said hammers, and said timing means synchronous with the movement of said type carrier including another decoder having the address in said register applied thereto for producing said signals for de-energizing said electromagnets after they have been previously energized.

7. A high speed printer as set forth in claim 6, and including additional timing means synchronous with the movement of said type carrier for inhibiting the one of said decoders effective for causing a de-energization of any of said electromagnets for setting times of the electromagnets less than one print scan duration and more than the duration of two print scans so that the electromagnet remains energized for a time between one and two print scans.

8. A high speed printer as set forth in claim 3, and including a storage unit having a section for retaining data to be printed by said hammer and also including a section for maintaining the image of the chain characters passing the print hammer, and means for comparing the chain image and the data to be printed and for energizing the electromagnet to fire the hammer when there is a compare.

'9. A high speed printer as set forth in claim 8, said data to be printed and said chain images in said storage unit each having an address, means for storing an address which has a definite relationship to and is derivable from the address in said storage unit of the data to be printed, said means acting in timed relationship with the movement of said type carrier including a decoder which has the address in said register applied thereto to selectively energize said electromagnet for firing said hammer, and said timing means synchronous with the movement of said type carrier including another decoder having the address in said register applied thereto for producing said signal for de-energizing said electromagnet after it has been previously energized.

10. A high speed printer as set forth in claim 9, and including additional timing means synchronous with the movement of said type carrier for inhibiting the one of said decoders effective for causing a de-energization of said electromagnet for a setting time of the electromagnet less than one print scan duration and more than the duration of two print scans so that the electromagnet remains energized for a time between one and two print scans. 

1. A high speed printer comprising, in conbination: a moving type carrier having a series of print characters thereon, a print hammer disposed to impact with said type carrier for printing said print characters in a print position located in alignment with said hammer, a hammer driver motor for firing said hammer upon being energized, means for driving said type carrier so as to move said print characters successively into alignment with said hammer with a print scan being determined from the time when one print character of the type carrier is in alignment with said hammer to the time when the next print character on the type carrier is in alignment with said hammer, means acting in timed relationship with the movement of said type carrier for selectively energizing said motor so as to fire said hammer, timing means synchronous with the movement of said type carrier for producing a signal which is subsequent to the firing of said hammer by a time different than one print scan duration, and means responsive to said signal for de-energizing said motor within the duration of said last-named print scan.
 2. A high speed printer as set forth in claim 1, said hammer driver motor constituting an electromagnet.
 3. A high speed printer as set forth in claim 2, said type carrier constituting an endless chain.
 4. A high speed printer as set forth in claim 3, said printer including additional print hammers disposed in a line with said first-named print hammer and each actuated by an electromagnet, said electromagnets for said additional print hammers being energized and being de-energized by the same means as the electromagnet for said first-named print hammer.
 5. A high speed printer as set forth in claim 4, and including a storage unit having a section for storing data to be printed by said hammers and also including a section for storing the images of the chain characters passing the various print hammers, and means for comparing the chain images and the data to be printed and for energizing the respective electromagnets to fire the respective hammers when there is a compare.
 6. A high speed printer as set forth in claim 5, said data to be printed and said chain images in said storage unit each having an address, means for storing an address which has a definite relationship to and is derivable from the address in said storage unit of the data to be printed, said means acting in timed relationship with the movement of said type carrier including a decoder which has the address in said register applied thereto to selectively energize said electromagnets for firing said hammers, and said timing means synchronous with the movement of said type carrier including another decoder having the address in said register applied thereto for producing said signals for de-energizing said electromagnets after they have been previously energized.
 7. A high speed printer as set forth in claim 6, and including additional timing means synchronous with the movement of said type carrier for inhibiting the one of said decoders effective for causing a de-energization of any of said electromagnets for setting times of the electromagnets less than one print scan duration and more than the duration of two print scans so that the electromagnet remains energized for a time between one and two print scans.
 8. A high speed printer as set forth in claim 3, and including a storage unit having a section for retaining data to be printed by said hammer and also including a section for maintaining the image of the chain characters passing the print hammer, and means for comparing the chain image and the data to be printed and for energizing the electromagnet to fire the hammer when there is a compare.
 9. A high speed printer as set forth in claim 8, said data to be printed and said chain images in said storage unit each having an address, means for storing an address which has a definite relationship to and is derivable from the address in said storage unit of the data to be printed, said means acting in timed relationship with the movement of said type carrier including a decoder which has the address in said register applied thereto to selectively energize said electromagnet for firing said hammer, and said timing means synchronous with the movement of said type carrier including another decoder having the address in said register applied thereto for producing said signal for de-energizing said electromagnet after it has been previously energized.
 10. A high speed printer as set forth in claim 9, and including additional timing means synchronous with the movement of said type carrier for inhibiting the one of said decoders effective for causing a de-energization of said electromagnet for a setting time of the electromagnet less than one print scan duration and more than the duration of two print scans so that the electromagnet remains energized for a time between one and two print scans. 